16 MARINE FAUNA 01' ST. ANDREWS. 



portions as possible; but this is their only approximation to 



each other; in their other characters they differ to a con- 

 siderable extent. The colour of II. regularis in the dried 

 state is milk-white ; that of'//. WIntoshii is nut-brown. An- 

 other important difference is, that while the skeleton of II. 

 regular!* is remarkable for its symmetry, that of //. M'Intoshii 

 is irregular to a very considerable degree." 



This form is not uncommon on the under surface of stones 

 in tide-runs and somewhat muddy pools not far from high- 

 water mark, at the East Rocks. Its greyish brown colour, 

 smooth surface, and prominent, well-defined oscula distinguish 

 it at first sight from its allies. 



Halichondria incrustans, Esper ; liowerb. vol. ii. p. 249. 



Occasionally found under stones near low-water mark, 

 especially at the East Rocks. It forms a thickish crust ; and 

 the spicula very much resemble one of the knobbed walking- 

 sticks which taper from above downwards. 



Suborder III. KERATOSA. 



Chalina oculata, Pallas; Bowerb. vol. ii. p. 361. 



Thrown in great profusion on the West Sands after storms ; 

 and small specimens are also found under the ledges of rocks 

 near low-water mark. The shape of the specimens varies 

 much : some are flattened and much divided into branches of 

 various sizes, either narrow or broad; others have their 

 branches matted together so as to form a connected and 

 somewhat coarse "gorgonian" appearance, more or less sepa- 

 rated at the tip. In some the branches arise mostly from one 

 side of an unbroken prolongation of the sponge-tissue. One 

 grows on a valve of Mytilus modiolus, and has a mass of 

 Halichoiiilriu jKiuii-in round a branch at its base. Another 

 envelops the stem and branches of Delesseria sanguined, the 

 leaves of which appear here and there from the centre of 

 the sponge. Many are attached to small rolled stones. 



